Resize tokenizer text input after pasting

Summary:
Fixes T5251. We don't recompute tokenizer metrics accurately after a paste event.

Listen for paste events and redraw the input.

Test Plan: Pasted long text into a tokenizer in Safari, Firefox and Chrome.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T5251

Differential Revision: https://secure.phabricator.com/D10442